1 Field of the Invention
The present invention relates to a sheet feeding apparatus and an image forming apparatus, and particularly, to a configuration of a regulating portion that regulates a movement of a sheet.
2. Description of the Related Art
Hitherto, many sheet feeding apparatuses that adopt various sheet feeding techniques such as an air sheet feeding technique or a retarding roller sheet feeding technique have been proposed. Recently, in such sheet feeding apparatuses, there has been a demand for a sheet feeding apparatus that includes a large capacity of an accommodation deck and continuously supplies many sheets to an image forming portion.
As such a sheet feeding apparatus, there is known a sheet feeding apparatus employing an air sheet feeding technique. The sheet feeding apparatus includes a large capacity of an accommodation deck and feeds sheets accommodated in the accommodation deck by air (see U.S. Patent Application Publication No. 2010/0194031 A1). Then, in the sheet feeding apparatus, for example, an air sheet feeding type sheet feeding portion 400 is disposed above an accommodation deck (not illustrated) accommodating the sheets as illustrated in FIGS. 14A and 14B. Then, the sheet feeding portion 400 includes an absorption conveying belt 21, an absorption duct 51 disposed inside the absorption conveying belt 21, and an absorption fan (not illustrated) which allows the inside of the absorption duct 51 to have a negative pressure.
The accommodation deck is equipped with a lifting and lowering platen 12 which places a plurality of sheets S thereon and is lifted or lowered and a tail end regulating plate 13 which regulates the tail end positions of the plurality of placed sheets S. Further, a loosening nozzle 33 and a separating nozzle 34, which are provided on the downstream of the accommodation deck in the sheet feeding direction so as to blow air from the leading ends of the sheets S, are provided so as to loosen or separate the sheets S while being blown up. Then, the loosening nozzle 33 and the separating nozzle 34 are connected with an air supply unit 401 with a loosening and separating fan (not illustrated), and air is supplied to the loosening nozzle 33 and the separating nozzle 34 by the air supply unit 401.
Next, a sheet feeding operation of the sheet feeding portion 400 of the related art will be described. When the sheet feeding operation starts, the lifting and lowering platen 12 having the sheets S placed thereon starts to be lifted until the uppermost sheet Sa of the plurality of placed sheets S reaches a predetermined position around the opening of the loosening nozzle 33 illustrated in FIG. 14A. Subsequently, when a sheet feeding instruction is received, the separating fan of the air supply unit 401 starts to rotate.
Accordingly, loosening air and separating air start to blow from the loosening nozzle 33 and the separating nozzle 34 as indicated by the arrows a and b toward the side end of the upper portion of the plurality of stacked sheets S. Here, the backward movement of the sheet S is regulated by the tail end regulating plate 13. Accordingly, when air blows, the blowing air enters between the sheets S, so that the upper portion of the stacked sheets S is blown up so as to loosen the sheets S.
On the other hand, at the time point at which the sheet feeding instruction is received, the absorption fan starts to rotate, and hence the inside of the absorption duct 51 becomes a negative pressure state. For this reason, when an absorption shutter (not illustrated) provided inside the absorption duct 51 is opened, the uppermost sheet Sa is absorbed onto the absorption conveying belt 21. Furthermore, at this time, it is possible to reliably separate the uppermost sheet Sa and the lower sheet from each other by the effect of the separating air flow formed below the absorption conveying belt 21 by the separating nozzle 34.
Subsequently, the absorption conveying belt 21 rotates according to an image forming timing of an image forming portion (not illustrated), and the uppermost sheet Sa is delivered to a pair of drawing rollers (not illustrated) disposed at the downstream of the absorption conveying belt 21 in the sheet feeding direction, thereby completing the feeding of the uppermost sheet Sa. Furthermore, at the time point at which the sheet Sa is delivered to the pair of drawing rollers, the absorption shutter is closed and the inside of the absorption duct 51 becomes a negative pressure state, thereby preparing the next sheet feeding operation. Hereinafter, this operation is repeated.
Here, in the sheet feeding apparatus including a large capacity of the accommodation deck, the tail end regulating plate as the regulating portion which regulates the movement of the sheet is generally provided so as to be movable to the tail end regulating position in response to the size of the sheet. Then, when the sheets are placed on the lifting and lowering platen, the tail end regulating plate is moved and set so as to match the tail ends of the placed sheets. Further, the accommodation deck is equipped with a side end regulating plate as a regulating portion which regulates the position of the sheet in the width direction perpendicular to the sheet feeding direction, and when the sheet is placed on the lifting and lowering platen, the side end regulating plate is also moved and set so as to match the side ends of the placed sheets.
However, for example, when moving the tail end regulating plate, a gap may be formed between the tail end regulating plate and the sheet when the movement of the tail end regulating plate is not sufficient or the tail end regulating plate is set while the sheet is not placed on a lifting and lowering platen in a straight way. Then, when air blows to the sheets while the gap is formed between the sheet and the tail end regulating plate in this way, the sheet S which is blown up by the air is retracted in the direction opposite to the sheet feeding direction by the gap between the sheet and the tail end regulating plate 13 as illustrated in FIG. 14B.
As a result, the balance between the separating air, the loosening air, and each air flow from the absorption duct collapses, so that the sheet S is unstably blown up. Accordingly, the sheet may not be normally absorbed onto the absorption conveying belt 21 or a plurality of sheets may be absorbed onto the absorption conveying belt 21. In this case, a problem arises in which a feeding failure occurs in the sheet S or a double feeding occurs in the sheet S.
Furthermore, this problem arises not only in a sheet feeding apparatus employing the air sheet feeding technique, but also a retarding roller type sheet feeding apparatus which returns double-fed sheets toward the tail end regulating plate by a retarding roller. That is, even in a case of the retarding roller type sheet feeding apparatus, when a gap is formed between the sheet and the tail end regulating plate, the sheet which is returned by the retarding roller may be retracted by the gap between the tail end regulating plate and the sheet. Then, in such a case, a feeding failure may occur in the sheet.
Therefore, the invention is made in view of such circumstances, and it is desirable to provide a sheet feeding apparatus capable of reliably feeding a sheet even when a gap is formed between the sheet and a regulating portion, and an image forming apparatus.